The present invention relates to a device for recovering hydrocarbon vapors in fuel dispensing systems.
In fuel delivery systems, in particular when refueling the tank of an automotive vehicle through a filling nozzle, a portion of the fuel entering the tank evaporates due to the lower vapor pressure of the fuel. The vapor escapes through the fuel filling tube into atmosphere. This has to be prevented primarily because of the cancerous properties of the hydrocarbon. For this purpose a gas recovery system is provided to be used at all gas stations for returning the vapors occurring through a conduit to the stationary fuel container from which the fuel is pumped to the filling nozzle. Principally, the liquid volume of fuel delivered to the vehicle tank approximately equals the gas volume to be returned to the stationary tank.
According to a prior art device, a vacuum pump is provided in the vapor recovery line for extracting the vapor and a valve is provided comprising a pair of floaters, wherein the position of a first floater is adjustable in proportion to the fuel volume to be delivered which position is transmitted to the second floater by means of a rod or a permanent magnet which second floater controls the gas volume to be returned in the gas recovery line. In this system the fuel volume represents the controlling parameter and the control of the gas volume is performed mechanically. The mechanical system does not operate precisely enough.
It is an object of the present invention to provide a device of recovering hydrocarbon vapors such that the gas recovery volume is controlled highly accurately and reliably.
According to the invention the object is solved by the features of the claims. The subclaims refer to features of preferred embodiments of the invention.
According to the invention the return flow of the vapors is controlled by a proportional throttle valve which is arranged between the vapor line and the vacuum pump. The volume flow of the fuel delivered is measured, preferably by the electronic fuel meter of the fuel pump. The signal is used as a desired value. In addition, the gas volume flow returning to the stationary container is measured to provide a signal for the actual value. From a comparison of both the desired and the actual value, an error signal is generated which is used to control the solenoid of the proportional valve.
Still further, the atmospheric air pressure may be measured to correct the control signal for the solenoid in response to the atmospheric pressure. This increases the accuracy of the gas volume control as the volume of gas recovered is a function of the pressure difference between the atmospheric pressure and the vacuum pressure.
As mentioned before, in many cases the volume flow of the vapor returned equals the fuel volume delivered. This ratio can be varied when the signal of the electronic meter of the fuel pump is varied correspondingly so that the gas volume to be controlled may be adjusted to be higher or lower. Moreover the proportional throttle valve may be adjusted in response to the air temperature measured. Accordingly the gas volume flow may be decreased when less fuel evaporates when the air temperature is less.
The arrangement according to the invention still provides for the advantage that vacuum fluctuations in the system as well as atmospheric air pressure fluctuations are sensed and the control of the valve solenoid is accordingly corrected. A further advantage is provided by eliminating mechanical connections between the fuel line and the gas recovery line which could give reason that, for example, liquid fuel may enter the gas recovery line.
The structure of the proportional throttle valve according to the invention results in a high control accuracy. The valve according to the invention can be mounted under severe conditions of environment and operates safely. In particular, the valve has a small hysteresis to precisely control the fuel vapor to be returned and to reduce the bleeding of vapors through the vent pipe of the stationary fuel tank. The valve is explosion-safe which is particularly useful with respect to the highly explosive fuel vapors, and can be mounted underneath the installation subjected to wet conditions.
The tandem piston arrangement of the valve according to the invention results in a very accurate central guiding of the valve member to reduce the eccentric forces acting there-on. More specifically, the valve according to the invention has an extremely small hysteresis. This is even improved by the special sealing means for the piston of the valve housing and by providing antifriction guiding faces on the seal.
The throttle area provided between the passage and the connecting rod of the tandem piston limits the volumetric flow of fluid through the passage even when the valve is fully opened. This reduces the environmental load by less vapor escaping through the stationary tank vent pipe.
The tandem piston is actuated through a force transmitting member such as a plunger which can be actuated by an electromagnetical, mechanical or fluid operated actuator. Preferably, the valve housing and the actuator are separated from each other by an intermediate body serving as a geometrical and thermical isolation.
The dual seal arrangement provided by the tandem piston makes the valve particularly useful to be mounted in fuel vapor recovery systems.
In order that the invention may be fully understood a preferred embodiment of the invention will now be described by way of example, with reference to the accompanying drawings. The drawings show: